1. Field of the Invention
The present invention relates to a camera-shake correction apparatus and an imaging apparatus including the camera-shake correction apparatus.
2. Description of the Related Art
A camera-shake correction apparatus or an imaging apparatus having a camera-shake correction function can be equipped with a gyro sensor (i.e., an angular speed sensor) to detect a camera-shake amount applied to the apparatus. The gyro sensor includes a piezoelectric element or a comparable vibratory member that vibrates at a predetermined frequency. The gyro sensor can convert a Coriolis force into a voltage to obtain angular speed information. Then, the gyro sensor integrates the obtained angular speed to calculate the camera-shake amount. The camera-shake correction can be performed by moving a camera-shake correction member (e.g., a shift lens or an image sensor) that can optically shift the angle of view in a predetermined direction so as to cancel the calculated camera-shake amount.
In such a camera-shake correction apparatus, to adequately correct vibrations that may be caused by a shaking hand or other vibrations having similar frequency distributions, a suitable camera-shake detection sensor is required and a camera-shake correction optical system needs to be adequately selected. Further, it is required to adequately set a response frequency band for the above-described sensor. Similarly, it is required to adequately set a response frequency band for a driving mechanism.
Accordingly, in a case where the above-described camera-shake correction apparatus is fixed on a tripod, the camera-shake correction member may unnecessarily perform a camera-shake correction in response to a low-frequency drift signal (i.e., fluctuation) that may be output from the camera-shake detection sensor. The low-frequency drift signal has no relationship with the shake of the imaging apparatus. In this case, the fluctuation of an image formed on the image sensor may rather be increased.
To solve the above-described drawbacks, for example as discussed in Japanese Patent Application Laid-Open No. 11-38461, if the camera-shake detection sensor generates a very small output signal, it can be regarded that the imaging apparatus is fixed or attached to the tripod. Therefore, in this case, execution of the camera-shake correction is cancelled.
The conventional technique requires a vibration detection unit configured to detect a vibration amount applied to the imaging apparatus and a supporting state determination unit configured to determine a supporting state of the imaging apparatus by determining whether the imaging apparatus is held by a user's hand or attached to the tripod. The supporting state determination processing to be performed by the conventional technique includes comparing a camera-shake signal obtained by the vibration detection unit with a predetermined determination level, then updating a count value if the camera-shake signal is equal to or greater than the determination level, or equal to or less than the determination level, and finally identifying the supporting state of the imaging apparatus by determining whether the count value is equal to or greater than a predetermined value.
Further, the conventional technique does not perform a camera-shake correction operation if the camera-shake detection sensor generates a very small output signal before starting exposure processing. This is effective to prevent the camera-shake correction operation from being unnecessarily performed in response to the low-frequency drift signal that may be output from the camera-shake detection sensor in a state where the imaging apparatus (e.g., a camera) or an optical device is fixed to the tripod. In this case, if a camera-shake displacement is small in amplitude, the conventional technique always cancels the camera-shake correction operation and holds the lens at an optical center position.
However, in a state where the camera-shake detection sensor generates a very small output signal after starting the exposure processing, if the camera-shake correction member is moved to the optical center position during the exposure processing, a captured image may be a fluctuated image that includes a change in the angle of view. Further, when the camera-shake correction operation resumes again from a state where the camera-shake correction operation is stopped, the camera-shake correction operation cannot be accurately performed if a lens target position is an edge of a driving range of a camera-shake correction lens.